Highly concentrated, stable, and safe diacyl peroxide and peroxydicarbonate emulsions with a low chemical oxygen demand value

ABSTRACT

The invention relates to highly concentrated aqueous emulsions of peroxides comprising an anti-freeze agent, a polyvinyl acetate with a degree of hydrolysis between 45 and 80%, and optionally a non-ionic surfactant with an HLB value greater than 10 selected from alkylene oxide block-copolymers, ethoxylated fatty alcohols, and ethoxyfated fatty acids. The emulsions have a low COD value and are safe, storage stable, and generally applicable.

The invention relates to aqueous emulsions of diacyl and/orperoxydicarbonate peroxides comprising a protective colloid, a non-ionicemulsifier, and an anti-freeze agent.

Such peroxide emulsions are known from British patent GB 2 068 008,which discloses emulsions comprising a peroxydicarbonate, a non-ionicemulsifier, and a protective colloid. The non-ionic emulsifier can bechosen from a wide variety of compounds including an ethoxylated fattyalcohol and most preferably an ethoxylated fatty acid. Similarly, theprotective colloid can be selected from a myriad of components. Theperoxydicarbonate emulsions disclosed in GB 2 068 008 have relativelylow peroxide concentrations of up to 30% by weight (% w/w). It is knownin the art that if the peroxide concentration is increased, an increasein the volume average peroxide droplet size (d50) and an increase in the99 percentile droplet size distribution (d99) will result or, evenworse, separation of the peroxide from the aqueous emulsion. In anycase, the values for d50 and d99 will increase over time, eventuallyrendering the emulsion unstable and unsafe. Also the viscosity is knownto increase to an unacceptable level if the peroxide concentration inconventional formulations is increased.

The stability and safety of emulsions with 40% w/w peroxydicarbonate isimproved when propylene glycol is added as anti-freeze agent in anamount of 25% by weight, as is described in JP2001064321. The chemicaloxygen demand (COD) value of in particular the aqueous phase of theseemulsions, however, is unacceptably high, which is highly undesirableparticularly from an environmental point of view.

It is an object of the present invention to provide an aqueous emulsionof a diacyl peroxide and/or a peroxydicarbonate with a high peroxideconcentration which has an improved COD value of the aqueous phase,particularly in relation to the amount of peroxide in the organic phase,which emulsion also has acceptable stability, viscosity, and safetycharacteristics.

We have now found that, surprisingly, improved aqueous peroxideemulsions can be produced and applied by a proper combination of diacylperoxide and/or peroxydicarbonate, protective colloid, non-ionicsurfactant, and anti-freeze agent. These emulsions not only have a lowCOD value, they also are more economical to produce and were found to beable to improve the properties of the polymer produced therewith.

The invention consists of a peroxide emulsion wherein the concentrationof the peroxide ranges from 52.5 to 75% by weight and the protectivecolloid is a partly saponified polyvinyl acetate having a concentrationof from 0.01 to 2.5% by weight, wherein the polyvinyl acetate has adegree of hydrolysis of at least 45 and at most 80%, and with astabilizing amount of one or more non-ionic surfactants and/or one ormore anti-freeze agents such that the result is a stable and safeformulation with an aqueous phase that has a low COD value. Despite thehigh concentration of the peroxide, such an emulsion has d50 and d99values which do not substantially change over time, resulting in a verystable emulsion. Also, such emulsions were found to be storage safe andto have acceptable viscosity. Moreover, these emulsions generally havesmall peroxide droplet sizes, which is advantageous if they are used inpolymerization reactions for which they are suitable. Such small dropletsizes and droplet size distributions enable better control of theprocess of polymerization, as the peroxide efficiency is enhanced,thereby improving the space-time yield of the said process. In theemulsion of the invention the amount of polyvinyl acetate (PVAc) can bevery low, e.g., lower than 1%, which substantially decreases the cost ofsuch an emulsion, as the PVA is expensive, and which reduces the CODvalue of the aqueous phase. Although the invention is suitable toproduce emulsions of diacyl peroxides, peroxydicarbonate, and emulsionscomprising a mixture of these two classes of peroxides, it isparticularly suitable for preparing emulsions of peroxides that, whendiluted to a concentration of 75% in isododecane, have aself-accelerating decomposition temperature (as determined according toconventional UN regulations) of 10° C. or less. Such peroxides ormixtures of peroxides typically require the use of anti-freeze agentswhen an emulsion is produced, resulting in emulsions with a high COD.More preferably, the emulsions according to the invention comprise atleast one or more peroxydicarbonates, since here the reduction of theCOD value, compared to conventional emulsions, is greatest. Mostpreferably, the emulsions of the present invention comprise essentiallyonly one or more peroxydicarbonates.

The relatively low COD value of the aqueous phase of the emulsionensures that the environmental burden is substantially reduced. Theaqueous phase is defined as encompassing all constituents of theperoxide emulsion except for the peroxide itself and/or any organicdiluent of the peroxide. The said COD value is defined as the mg ofoxygen needed for oxidation of the organic compounds in 100 mg of theaqueous phase of the emulsion. The said COD value therefore depends onthe amount of organic compounds, e.g., the anti-freeze agents andprotective colloids, in the aqueous phase. The amount of anti-freezeadded to the aqueous phase of the emulsion can be determined by thereduction in freezing point of the aqueous emulsion. It is commonlyknown that the freezing point decreases by about 18.6° C. per mole ofanti-freeze dissolved in 100 g of water. In other words, emulsions maycontain anti-freeze agents with a relatively low molecular weight in asmaller weight fraction than high-molecular weight agents to give thesame freezing point decrease. The required freezing point decrease for aperoxide emulsion depends on the desired storage temperature, which isspecific for each peroxide. For, example, for a di(2-ethylhexyl)peroxydicarbonate this storage temperature is −15° C., as is disclosedin the brochure entitled “Initiators for High Polymers” with code1000225 from Akzo Nobel Chemicals B.V. If methanol and propylene glycolare compared, it is evident that fewer milligrams, of methanol thanmilligrams of propylene glycol are needed in the emulsion to obtain thesame decrease in freezing point. Consequently, also taking into accountthat about 1.3 mg and about 1.7 mg of oxygen are needed for theoxidation of, respectively, 1 mg of methanol and 1 mg of propyleneglycol, it is clear that the COD of the aqueous phase containingmethanol is substantially lower than the COD of the aqueous phasecontaining propylene glycol with an equal freezing point. An acceptableCOD value of the aqueous phase as far as an anti-freezing agent isconcerned is at most 50 mg oxygen per 100 mg aqueous phase, preferablyat most 40 mg oxygen per 100 mg aqueous phase, and most preferably atmost 30 mg oxygen per 100 mg aqueous phase.

It is noted that the present invention relates to emulsions that areliquid when stored at the recommended storage temperature. Hence, itdoes not relate to products that are also know as “frozen emulsions,”which are solids at the recommended storage temperature, and whichtypically contain very little or no anti-freeze.

The peroxide emulsions of the invention are concentrated, which isdefined here as emulsions wherein the amount of peroxide exceeds 40% byweight. Preferably, the concentration of peroxide in the emulsionsaccording to the invention is at least 52.5% w/w, more preferably atleast 55% w/w, and most preferably at least 60% w/w. The peroxideconcentration is at most 75% w/w, more preferably at most 70% w/w, andmost preferably at most 65% w/w. These peroxide emulsions will ensuresubstantially reduced freight and handling costs in comparison withconventional peroxide emulsions containing 40% w/w or less of peroxide.The safety aspects of the final emulsion predominantly determine thehigh end of the peroxide concentration range. It was found that a properselection of the water/anti-freeze content of the formulation willfurther enhance the safety characteristics. More specifically, whenproperly chosen, the water and the anti-freeze can dissipate the heat ofdecomposition of the peroxide.

The peroxide emulsions according to the invention preferably comprise aperoxide that is liquid or dissolved at −10° C., in particular aperoxide having a recommended storage temperature of 15° C. or less,more preferably a recommended storage temperature of 10° C. or less,even more preferably a recommended storage temperature of 0° C. or less,and most preferably a recommended storage temperature of −10° C. orless. Typically, the recommended storage temperature is specified by theproducer of the peroxide. If the recommended storage temperatureunknown, reference is made to the Akzo Nobel Chemicals B.V. brochure“Initiators for high polymers” with code 10737.

Peroxydicarbonates preferably used in the aqueous emulsions according tothe invention include: di-sec-butyl peroxydicarbonate (TRIGONOX® SBP),dibutyl peroxdedicarbonate (TRIGONOX® NBP), diisopropylperoxydicarbonate (TRIGONOX® IPP), di(2-ethylhexyl)peroxydicarbonate(TRIGONOX® EHP), (TRIGONOX® ADC), dibutyl peroxydicarbonate (TRIGONOX®NBP), bis(3-methoxybutyl)peroxy-dicarbonate,bis(isobutyl)peroxydicarbonate, dineopentyl peroxydicarbonate,bis(1-methylheptyl )peroxydicarbonate,bis[2-(2-methoxyethoxy)ethyl]peroxydicarbonate,bis(3-methoxy-3-methylbut-yl)peroxydicarbonate, andbis(2-ethoxyethyl)peroxydicarbonate. Other examples are dissolveddistearyl peroxydicarbonate and dicyclohexyl peroxydicarbonate. Anyappropriate inert phlegmatizing solvent can be used to dilute and/ordissolve any of the peroxydicarbonates. Such solvents are well known inthe art and include for instance isododecane.

As said above, suitable diacyl peroxides for use in the aqueousemulsions according to the invention are those that are liquid ordissolved at −10° C. Preferred diacyl peroxides include: diisobutyroylperoxide, di(3,5,5-trimethylhexanoyl)peroxide,di(2-ethylhexanoyl)peroxide, di(2-ethylbutanoyl)peroxide, anda-symmetrical diacyl peroxides, such as isobutyroyl octanoyl peroxide,isobutyroyl decanoyl per oxide, isobutyroyl lauroyl peroxide,2-ethylbutanoyl decanoyl peroxide, and 2-ethylhexanoyl lauroyl peroxide.The most preferred diacyl peroxides comprise at least one isobutyroylmoiety of the formula

The protective colloid to be used in the aqueous emulsions according tothe invention must be a PVAC with a degree of hydrolysis of at least 45,more preferably at least 48%, and most preferably at least 50%, and atmost 80%, preferably at most 70%, more preferably at most 62.5%, andmost preferably at most 60%. A PVAC with a degree of hydrolysis below45% cannot be used because such a PVAC is not soluble in the mixture ofwater and anti-freeze. A PVAC with a degree of hydrolysis above 80%resulted in emulsions with a too high viscosity. Instead of using justone type of PVAC, also a blend of two or more PVACs can be used. In thatcase the blend can be seen as just one PVAC of which the degree ofhydrolysis is the weight average degree of hydrolysis of the PVACs.Preferably, such a blend of PVACs does not comprise a PVAC with a degreeof hydrolysis below 45% or above 80%, for the above-mentioned reasons.Celluloses were found not to be suitable, since the level at which theyare to be used results in emulsions with a too high COD.

The amount of PVAC used in the emulsions according to the invention willdepend on the concentration and the types of peroxides and surfactantsused and the desired viscosity of the final emulsion. Typically, theamount of PVAC in the final emulsion will be at least 0.01% w/w,preferably at least 0.1% w/w, and most preferably 0.5% w/w, and at most2.5% w/w, more preferably at most 2.0% w/w, even more preferably at most1.5% w/w, and most preferably at most 1.0% w/w. The use of theseprotective colloids in combination with the above-mentioned surfactantsenables the production of concentrated, storage-stable, and safeperoxydicarbonate emulsions. An acceptable COD value of the aqueousphase as far as PVAC is concerned is at most 5 mg oxygen per 100 mgaqueous phase, preferably at most 3 mg oxygen per 100 mg aqueous phase,more preferably at most 2 mg oxygen per 100 mg aqueous phase, and mostpreferably at most 1.5 mg oxygen per 100 mg aqueous phase.

Further, it is advantageous to add a non-ionic surfactant to theperoxide emulsion. In this specification, the term “surfactant” refersto the surface-active chemical that is to be used in the peroxideformulations according to the invention and that influences theinterfacial surface tension between the water and the peroxide phase.Such compounds are also known as “emulsifiers.” Preferably, the aqueousperoxide emulsion according to the invention contains only onesurfactant with an HLB value of 15 or higher. More preferred aresurfactants with an HLB value of at least 16, and most preferred aresurfactants with an HLB value of at least 17. If so desired, a mixtureof surfactants may be used. In that case, the combined surfactantsshould have an HLB value of 15 or higher, while it is preferred that allsurfactants used have an HLB greater than 10, preferably greater than12.5, and more preferably of 15 or higher, because surfactants with alower HLB value can have an adverse effect on the viscosity of the finalemulsion. As surfactants with an HLB of less than 10 undesirablyincrease the viscosity of the emulsion, sorbitan esters such as sorbitanoleate (HLB 4.3) and sorbitan laurate (HLB 8.5) are not suitable. HLBvalue stands for the hydrophilic-lipophilic balance, as described in“The Atlas HLB-System, a time saving guide to emulsifier selection,”published by Atlas Chemical Industries Inc., 1963. For blends ofsurfactants the HLB value is calculated from the weight ratio of thecomponents, as is also mentioned in this publication.

The non-ionic surfactant or surfactants that can be used in the aqueousemulsions according to the invention are alkylene oxideblock-copolymers, ethoxylated fatty alcohols, and ethoxylated fattyacids. The preferred surfactants are ethoxylated fatty alcohols andethoxylated fatty acids with an HLB value greater than 15. Mostpreferred are such ethoxylated fatty alcohols. Examples of suitableethoxylated fatty alcohols include ethoxylated lauryl alcohol, e.g.,with a degree of ethoxylation of 23, having an HLB-value of 16.9, andobtainable from ICI as BRIJ® 35, ethoxylated dodecyl alcohol, such asREMCOPAL® 20, ethoxylated myristyl alcohol, ethoxylated cetyl alcohol,ethoxylated oleyl alcohol, ethoxylated mixtures of alcohols, such asETHYLAN® CO35, which is the ethoxylated product of a mixture of palmiticalcohol and oleyl alcohol, ethoxylated alcohols derived from coconutoil, palmitic acid, and/or tallow, and ethoxylated stearyl alcohol,e.g., with a degree of ethoxylation of 80 with an HLB-value of 18.5, andobtainable from Akzo Nobel as BEROL® 08. These products were found to bepre-eminently suited to make emulsions with good stability, safety, andviscosity properties at high peroxydicarbonate concentrations. Even withPVA concentrations below 1.0% w/w, the average droplet size of theperoxide is extremely small—generally smaller than 4 μm—with arelatively narrow droplet size distribution. Preferably, the amount ofthe surfactant or the combination of surfactants in the final emulsionis at least 0.01% w/w, preferably at least 0.02% w/w, and mostpreferably at least 0.05% w/w, and at most 5% w/w, preferably at most 2%w/w, and most preferably at most 1% w/w. An acceptable COD value of theaqueous phase as far as the surfactant is concerned is at most 20 mg.oxygen per 100 mg aqueous phase, preferably at most 10 mg oxygen per 100mg aqueous phase, more preferably at most 5 mg oxygen per 100 mg aqueousphase, and most preferably at most 2 mg oxygen per 100 mg aqueous phase.Instead of the surfactant, or together with the surfactant, ananti-freeze is to be used in the emulsions according to the invention,so that the emulsion is pourable and/or pumpable at the recommendedstorage temperature and lower, which as can be gleaned from the brochureentitled “Initiators for High Polymers” with code 1000225 from AkzoNobel Chemicals B.V., is specific for each peroxide-containing phase.The amount of freezing point suppressant to be used will depend on thetype of anti-freeze, or mixture of anti-freeze agents, used. Suitably,first a mixture of the anti-freeze and water is made which contains asufficient amount of the anti-freeze to be pourable at the indicatedtemperatures. This mixture can then be used in the further process tomake the emulsions. Although use can be made of most antifreeze agents,such as salts and organic compounds, it is preferred to use organiccompounds selected from methanol, ethanol, propanol, isopropanol,glycol, propanediol, and glycerol, since it is known that such compoundswill have hardly any effect on polymerization processes in whichperoxide emulsions are used. Most preferably, methanol is used asanti-freeze, as the COD value of the aqueous phase is relatively low(vide supra) and, furthermore, because agents such as ethylene glycol,propanol or propane are more likely to end up in the polymer that isformed when aqueous emulsions are used as a source of free radicals in apolymerization process, resulting in less desirable organolepticproperties of the polymer. Also combinations of two or more anti-freezeagents can be used in the emulsions according to the invention. If, forexample, ethylene glycol is added in a relatively low amount to amixture of water and methanol, the flammability will be positivelyinfluenced, as the total mixture will be less flammable at the sametemperature. It is noted that if the COD value of the aqueous phaseshould be too high due to the presence of the methanol, then someinorganic salts can be substituted for the organic compound. The amountof anti-freeze is preferably chosen such that the aqueous phase does notfreeze at a temperature of −10° C., preferably the emulsion does notfreeze at a temperature of −15° C., more preferably the emulsion doesnot freeze at a temperature of −20° C.

The compositions according to the invention contain a sufficient amountof the surfactants and/or anti-freeze agents for the desired stable andsafe aqueous peroxide emulsions to result.

The emulsions according to the invention may, if so desired, compriseone or more thickeners in a concentration up to 2% w/w in order tocontrol the viscosity of the composition. If used, the thickenerpreferably makes up less than 1% w/w of the emulsion. Non-limitingexamples of thickeners useful in the formulation are xanthan gum, Arabicgum, and alginates. However, thickeners are preferably omitted from theaqueous emulsions.

In addition to the above-mentioned compounds, the compositions accordingto the invention can also comprise other “standard” additives, includingpH-adjusting agents such as calcium oxide or phosphate buffers,sequestering agents, and, if desired, biocides, e.g. fungicides. Theconcentration of these additives will depend on the desired effect andthe other ingredients in the emulsion. Given the information presentedhere, the skilled man will have no problem selecting appropriateconcentrations of the individual ingredients in the emulsions of choice,as they will adversely affect the COD value of the aqueous phase.

What is meant by storage stable emulsions is that the products do notseparate at the storage temperature and have a volume averageperoxydicarbonate droplet size (d50) and a 99 percentile of the dropletsize distribution (d99) which do not change by more than 5 μm duringtwelve weeks of storage. Preferably, the change in d50 is less than 3μm, more preferably less than 2 μm and most preferably less than 1 μm,since changes in droplet size will influence the viscosity and furtherstorage stability of the emulsion, while also the polymerization processcan be adversely influenced when larger peroxide droplets areintroduced, e.g., by an increased number of fish-eyes. It is also forthis reason that the d50 of the droplet size distribution should bebelow 10 μm, while a d50 of less than 5 μm, particularly less than 4 μm,is preferred. The droplet size is determined by means of a lightscattering technique, using a Malvern® Easy Sizer.

As mentioned above, it is important that the concentrated peroxideemulsions according to the invention have a viscosity that allows easyhandling and use. In practice, this means that the product should have aviscosity of less than 1,500 mPa·s, when measured at the recommendedstorage temperature using an Erichsen viscometer, model 332 (0-1,500mPa·s). Preferably, the Erichsen viscosity is less than 500 mPa·s.Alternatively, suitable emulsions were found to have a viscosity below5,000 mPa·s when measured at the same temperature, using a BrookfieldLVT with spindle sp3 at 12 rpm. Preferably, the emulsions will have aBrookfield viscosity of less than 3,000 mPa·s.

As is well-known, peroxides are thermally labile organic compounds.Because the decomposition of peroxide is exothermic, it is hazardouswhen the heat of decomposition cannot be dissipated, e.g., by heat lossto the surrounding area. When heat build-up occurs, the decompositionreaction eventually becomes uncontrollable and potentially dangerous. Toavoid such undesired situations, the peroxide is typically formulatedwith one or more phlegmatizing agents, such as inert organic materials,including water. Aqueous peroxide emulsions are generally consideredsafe products, because the peroxide is dispersed in the water phase,which is well-suited to the removal of the heat of decomposing peroxidemolecules, e.g., by convection and/or evaporation. However, it wasobserved that many peroxide emulsions according to prior artformulations suffer from the drawback that they show phase separationupon heating, particularly at temperatures where water evaporationbecomes noticeable. If so, the peroxide separates out and forms a highlyconcentrated peroxide phase the heat of decomposition of which is notdissipated. As a result, such aqueous peroxide emulsions can be ashazardous as the neat peroxide. One of the objects of the emulsionsaccording to the invention therefore was to develop formulations that donot form a significant amount of a hazardous phase upon heating.

An emulsion in accordance with the invention is considered to be safe ifless than 10% by volume of one or more other phases is formed or, ifmore than 10% by volume of phase separation were to occur, none of thephases has a peroxide content such that the active oxygen content isgreater than 1% w/w. In a discriminating test for “safe” behaviour asample of the emulsion is kept at a temperature which is 35° C. abovethe well-known self-accelerating decomposition temperature (SADT) of theperoxide phase present in the emulsion for 8 hours.

The emulsions of the invention can be produced in a conventional manner.Typically, the compounds of the emulsion are mixed and/or homogenizedusing well-known equipment, such as colloid mills, perl mills, pressurehomogenizers, fluidizers, ultrasonic homogenizers, etc. Because many ofthe peroxydicarbonates are not stable at higher temperatures, the mixingand/or homogenizing should be done below a temperature of 15° C.,preferably well below the SADT.

The emulsions of the invention are preferably used in suspension oremulsion polymerization processes. However, they can also be used inother processes, such as polymer modification processes, cross-linkingreactions, mass polymerization processes, and curing processes of, forexample, unsaturated polyester resins. In these processes a variety ofmonomers and/or polymers can be reacted, including, for example,acrylates, vinyl esters, vinyl halides, vinyl ethers, vinyl aromaticcompounds, such as styrene, lower alkenes, polybutadiene,methacrylate-butadiene-styrene copolymers, and the like. The emulsionstherefore can be used, for example, in the mass polymerization of vinylchloride monomer (VCM). However, the emulsions are more preferably usedin suspension or emulsion polymerization processes wherein at least VCM,styrene or a (meth)acrylate is reacted. Most preferred is the use of theemulsions in the suspension polymerization process of predominantly VCM.The emulsions are only usable in these processes when they do notinfluence the properties of the resulting polymer, or do so only to avery limited extent. In the preferred VCM polymerization process, thismeans that hardly any fouling is observed and the PVC particle size,porosity, fish-eye number, and electrical properties are hardlyaffected.

It is noted that all weight percentages as used herein are based on theweight of the total aqueous emulsion.

As will be understood, the COD value is as small as possible, althoughit can vary over a wide range depending on the ingredients and theamounts in which they are used. Typically, the total COD of the aqueousphase is below 50 mg oxygen per 100 mg emulsion, preferably below 40 mgoxygen per 100 mg emulsion, more preferably below 30 mg oxygen per 100mg emulsion, even more preferably below 25 mg oxygen per 100 mgemulsion, and most preferably below 20 mg oxygen per 100 mg emulsion.More preferably, the COD value of the aqueous phase in relation to theamount of peroxide in the organic phase is below 2 mg oxygen per 100 mgemulsion per g peroxide, more preferably below 1.5 mg oxygen per 100 mgemulsion per g peroxide, even more preferably below 1.0 mg oxygen per100 mg emulsion per g peroxide, and most preferably below 0.5 mg oxygenper 100 mg emulsion per g peroxide.

The peroxide emulsions according to the invention and their uses arefurther illustrated in the following examples.

EXAMPLES

In the examples, the following products and abbreviations were used:

-   EHP=di(2-ethylhexyl) peroxydicarbonate (TRIGONOX® EHP ex Akzo Nobel)-   PVA65=62-68% saponified PVAC-   ESA=ethoxylated stearyl alcohol (HLB=18.5)

The aqueous peroxydicarbonate emulsions as described in the followingexamples comprise EHP, PVA65, optionally ESA, water, and methanol. Theamounts of each compound are given in the table.

Comparative Examples A and B

Comparative Examples A and B have an EHP concentration of 50% w/w, withthe weight percentage of PVA65 being reduced.

TABLE 1 Example A (reference) B EHP (as pure) (% w/w) 50 50 PVA65 (%w/w) 3.0 1.5 Balance water/methanol (% w/w/% w/w) 71/29 71/29 d99 1 day[micron] 2.5 3.3 d99 4 wks [micron] 2.8 7.2 d50 1 day [micron] 1.8 2.4d50 4 wks [micron] 2.0 3.2 Separation during storage (4 wks) none Veryslight Separation safety test OK FAIL Erichson [mPa · s] 220-205 120-90(0° C., 4 Weeks) Brookfield [mPa · s] 160-190 110 (0 C., 4 weeks)Brookfield [mPa · s] 2080 2304 (−10° C., 4 weeks)

From Comparative Examples A and B in Table 1, it is clear that theaverage droplet size (d50) grows when less PVA65 is used, as does the 99percentile droplet size distribution (d99). Also, at lower PVAconcentrations an unsafe emulsion results, as follows from theseparation safety test as described above. Also more concentratedperoxide emulsions wherein water was replaced by peroxide were found tobe unsafe and suffer from viscosity problems.

Examples 1-3

In Example 1 the amount of EHP is increased to 55% w/w, while for theemulsions of Examples 2 and 3, the EHP concentration is increased toabout 62 and 61% w/w, respectively. Examples 1-3 further comprise PVA65,ESA, water, and methanol.

TABLE 4 Example 1 2 3 EHP (as pure) (% w/w) 55 ca 62 ca 61 PVA65(% w/w)0.8 0.6 0.6 ESA (% w/w) 0.3 0.3 0.3 Balance water/methanol (% w/w/% w/w)69/31 69/31 69/31 Storage temperature is −15° C. d99, 1 day [micron] 2.82.5 2.5 d99, 2 weeks [micron] no data no data 2.5 d99, 4 weeks [micron]3.8 2.9 no data d99, 8 weeks [micron] 3.3 2.5 no data d99, 12 weeks[micron] 3.4 2.9 no data d50, 1 day [micron] 2.1 1.8 2.0 d50, 2 weeks[micron] no data no data 2.0 d50, 4 weeks [micron] 2.5 2.0 no data d50,8 weeks [micron] 2.4 2.3 no data d50, 12 weeks [micron] 2.6 2.2 no dataSeparation bottom (8 weeks) None None no data Separation top (8 weeks)None None no data Separation top (12 weeks) 1 mm no data no dataSeparation safety test OK OK no data Erichson [mPa · s] (−10° C., 2weeks) no data no data 370 (−10° C., 4 weeks) 300 475 390 (−10° C., 8weeks) 300 470 no data (−10° C., 12 weeks) no data 470 no data (−6° C.,12 weeks) 255 no data no data Brookfield [mPa · s] (−14° C., 2 wks) nodata no data 680 (−14° C., 4 wks) 720 2020 1010 (−14° C., 8 wks) 10502220 no data (−14° C., 12 wks) no data 2590 no data (−10° C., 12 wks)910 no data no data

All examples have low d50 and d99 values compared to the lowPVA-containing Example B. These values have not changed significantlyafter 12 weeks of storage. It follows that a small amount of ESA and asmall amount of PVA can be added to make a highly concentratedperoxydicarbonate emulsion with a small average droplet size and anarrow droplet size distribution with a good storage stability andsafety. It must further be noted that, despite the high EHPconcentration, the viscosity as represented by the Erichson andBrookfield viscosities is relatively low. The low amounts of ESA and PVAensure that an aqueous phase with a low COD value is obtained,especially a low COD value per gram of peroxide in the formulation. Alsothe use of methanol ensures that the COD value is low. It showsfurthermore that, when compared to conventional peroxide emulsions, thepresent emulsions surprisingly can be made with a lower COD per 100 g ofperoxide.

When evaluated in a conventional suspension polymerization process ofvinyl chloride monomer, it was surprisingly found that at equal peroxideloading and equal polymerization conditions, the polymer of theexperiments wherein emulsions according to the invention were usedshowed a significantly reduced number coarse PVC particles andsignificantly less fish-eyes, the term conventionally used in theindustry for defects observed when preparing foils of the polymer. Thereduction was seen not only in comparison with experiments in whichconventional solutions or pure peroxides were used, but, remarkably,also when compared with experiments wherein conventional peroxideemulsions were used. Illustrative of the effect is the comparison of theanalysis of the polymer resulting from a standard suspensionpolymerization of vinyl chloride using a 10 liter reactor wherein 2.87kg of vinyl monomer was polymerized using the peroxide emulsions ofExample 3 and Comparative Example A.

Peroxide emulsion from: Example A Example 3 Coarse PVC particles >800 μm(g) 4 2.4 D₅₀ of the PVC particles (wet analysis) 173 μm 177 μm Bulkdensity of the dried PVC powder 493 494 (kg/m³) Porosity of the driedPVC powder (%) 25.3 25.3 (conventional DOP absorption) Fish-eyes (dm⁻²)10-11 4-7

1. An aqueous emulsion, comprising an aqueous phase and aperoxide-containing phase, from 52.5 to 75% by weight of one or moreperoxides selected from the group of diacyl peroxides andperoxydicarbonates, from 0.01 to 2.5% by weight of a partly saponifiedpolyvinyl acetate having a degree of hydrolysis of at least 45 and atmost 80%, a stabilizing amount of one or more non-ionic surfactantshaving an HLB value of at least 10, and one or more anti-freeze agentssuch tat a storage stable and safe formulation results, wherein theaqueous phase has a total chemical oxygen demand (COD) of less than 20mg of oxygen per 100 mg of the emulsion, and the percentages by weightare based on the weight of the aqueous emulsion.
 2. An aqueous emulsionaccording to claim 1 wherein the non-ionic surfactant is an ethoxylatedfatty alcohol having an HLB value of at least
 15. 3. An aqueous emulsionaccording to claim 2 wherein the ethoxylated fatty alcohol is present inan amount from 0.001 to 5% by weight.
 4. An aqueous emulsion accordingto claim 1 wherein the anti-freeze agent is a compound selected from thegroup consisting of methanol, ethanol, isopropanol, glycol, propanediol,glycerol, and combinations thereof, and is used in a quantity such thatthe emulsion does not freeze at a temperature of −10° C.
 5. An aqueousemulsion according to claim 1 wherein the volume average droplet size ofthe peroxide-containing phase is less than 4 μm.
 6. An aqueous emulsionaccording to claim 1 wherein the peroxides comprise one or moreperoxydicarbonates.
 7. A process wherein an emulsion according to claim1 is used as a source of free radicals.
 8. A process according to claim7 wherein one or more ethylenically unsaturated monomers is polymerized.9. A process according to claim 8 wherein vinyl chloride is polymerized,optionally together with other monomers and/or in the presence of apolymer.
 10. An aqueous emulsion according to claim 1 wherein thenon-ionic surfactant is an ethoxylated fatty alcohol having an HLB valueof at least
 16. 11. An aqueous emulsion according to claim 1 wherein thenon-ionic surfactant is an ethoxylated fatty alcohol having an HLB valueof at least
 17. 12. An aqueous emulsion according to claim 2 wherein theethoxylated fatty alcohol is present in a amount from 0.001 to 1% byweight.
 13. An aqueous emulsion according to claim 10 wherein theethoxylated fatty alcohol is present in an amount from 0.001 to 1% byweight.
 14. An aqueous emulsion according to claim 11 wherein theethoxylated fatty alcohol is present in an amount from 0.001 to 1% byweight.
 15. An aqueous emulsion according to claim 1 wherein theanti-freeze agent is a compound selected from the group consisting ofmethanol, ethanol, isopropanol, glycol, propanediol, glycerol, andcombinations thereof, and is used in a quantity such that the emulsiondoes not freeze at a temperature of −15° C.
 16. An aqueous emulsionaccording to claim 1 wherein the anti-freeze agent is a compoundselected from the group consisting of methanol, ethanol, isopropanol,glycol, propanediol, glycerol, and combinations thereof, and is used ina quantity such that the emulsion does not freeze at a temperature of−20° C.